I just tried logging in to my GW2 account after not playing for quite some time to find out my account was terminated for “engaging in or assisting with gold or item sales for real-world money”, while I never did any of this.
The only possibility would be someone doing this on my account after hijacking it, but I would receive an email if someone tried logging in and my recent log ins show no IP’s I haven’t connected from myself.

I’m really curious how this could’ve happened and am very dissapointed as I never engaged in/assisted gold or item sales.

I really encourage you to contact Support by filing a ticket through the “Ask a Question” tab on that linked page. They will be able to assist you. For tips on what information to provide in a ticket, please read this post.

If you find you still need help after three days, feel free to post in the Tickets for Review thread, which is at the top of this Account Support sub-forum.